Peristaltic pump

ABSTRACT

A peristaltic pump having an adaptive pulsation profile.

BACKGROUND OF THE INVENTION

The present invention relates generally to peristaltic pumps and morespecifically to peristaltic pumps used in ophthalmic surgical equipment.

Peristaltic pumps work by compressing or squeezing a length of flexibletubing (sometimes between a fixed race) using a rotating roller head. Asthe roller head rotates, the rollers stretch and pinch off a portion ofthe tubing and push any fluid trapped in the tubing between the rollerin the direction of rotation. Peristaltic pumps are widely used inmedical applications because of their predictable flow properties.

Many factors influence the efficiency of peristaltic pumps, for example,pump motor torque, pump speed and pump tube flexibility. The efficiencyof a peristaltic pump is also dependent on how tightly the pump rollerscrush the tubing against the pump race. If the tubing is not collapsedcompletely by the rollers, not all of the fluid will be pushed furtherdown the tube. One characteristic of peristaltic pumps is that flow ratevaries in a cyclical manner. As a roller begins to pinch off the pumptubing, flow rate is reduced to minimum and then is accelerated to amaximum as the roller continues to sweep along the pump tubing segment.The pressure moves in an inverse relationship to the flow (Pressure ⇑ asFlow ⇓ or Pressure ⇓ as Flow ⇑). As the next roller begins to pinch offthe pump tubing, the cycle starts again. This cyclical variation in flowrate causes a cyclical variation in pressure within the fluid path, theeffects of which can be observed as pressure pulsations at the operativesite. Prior art peristaltic pumps have reduced the effects of thesepulsations by increasing the number of pump rollers and/or by taperingthe tubing, by introducing capacitance/compliance chambers into theaspiration line or by variable radius pumps. Increasing the number ofrollers and/or the use of variable radius pumps increases the cost andcomplexity of the pumping mechanism. Compliance or capacitance chambernegatively affect the performance (such as vacuum rise time) of thepump.

Accordingly, a need continues to exist for a method of reducingpulsations in a peristaltic pump that can be implemented without addingunnecessary complexity or compliance to the pumping system.

BRIEF SUMMARY OF THE INVENTION

The present invention improves upon prior art peristaltic pumps byproviding a peristaltic pump having an adaptive pulsation profile.

Accordingly, one objective of the present invention is to provide a highefficiency peristaltic pump.

Another objective of the present invention is to provide a peristalticpump that reduces pump pulsations.

Yet another objective of the present invention is to provide aperistaltic pump having an adjustable, adaptive pulsation profile.

These and other advantages and objectives of the present invention willbecome apparent from the detailed description, drawings and claims thatfollow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a surgical console that may be used withthe present invention.

FIG. 2 is a cross-sectional view of one embodiment of a peristaltic pumpof the present invention.

FIG. 3 is a plot of pump pressure/outflow over time for prior artperistaltic pumps.

FIG. 4 is a plot of pump pressure/outflow over time for the peristalticpump of the present invention.

FIG. 5 is a schematic representation of the pump of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

As best seen in FIG. 2, in one embodiment of the present invention, pump10 of the present invention generally includes pump motor 12, rollerhead 14, containing one or more rollers 16. Pump 10 is used incombination with cassette 18 having elastomeric sheet 20 applied to theexterior of relatively rigid body or substrate 22. Pump motor 12preferably is a stepper or D.C. servo motor. Roller head 14 is attachedto shaft 24 of motor 12 so that motor 12 rotates roller head 14 in aplane generally normal to the axis of shaft 24, and the longitudinalaxes of rollers 16 are generally radial to the axis of shaft 24. Shaft24 may contain shaft position encoder 25.

With respect to cassette 18, sheet 20 contains molded fluid channel 26that is generally planar, arcuate in shape (within the plane) and havinga radius approximating that of rollers 16 about shaft 24. Sheet 20 maybe made of any suitably flexible, easily molded material such assilicone rubber or thermoplastic elastomer. Sheet 20 is attached orbonded to substrate 22 by any suitable technique such as adhesive, heatfusion or mechanical crimping. Substrate 22 preferably is made of amaterial that is rigid with respect to sheet 20, such as a rigidthermoplastic, and may be made by any suitable method, such as machiningor injection molding.

As best seen in FIG. 5, pump 10 of the present invention may form partof console 112. Console 112 generally contains pump 10 that is in fluidcommunication with aspiration line 120 and aspiration exhaust line 134.Aspiration line 120 is connected to surgical handpiece 122 on one endand end 118 of aspiration line 120 opposite handpiece 122 is connectedto pump 10 so as to draw fluid through handpiece 122. Aspiration line120 is intersected between handpiece 122 and 118 by aspiration vent line124. In fluid communication with aspiration line 120 is sensor 126,which may be one of a variety of invasive or non-invasive pressure orflow sensors well-known in the art. Exhaust line 134 and vent line 124drain aspirated fluid into reservoir 128 contained within or on cassette18. Reservoir may additionally drain into drain bag 129, which may alsobe contained within or on cassette 18.

As best seen in FIGS. 3 and 4, the flow/pressure of peristaltic pumpsplotted against time has characteristic peaks and valleys. Each peak andvalley corresponds to a pump roller displacing fluid from a currentlyengaged pump segment. The minimum point (valley) corresponds to a rollerjust pinching off the pump segment (thus momentarily reducing flow), themaximum (peak) corresponds to flow being accelerated to a maximum rate.As seen in FIG. 3, prior art pumps can have large flow/pressurediscrepancies between the peaks and valleys, by way of example only, onthe order of 10-15 mm Hg.

Pump 10 of the present invention has an adaptive variable speed controlto accelerate rotation of rollers 16 on roller head 14 through knownminimum flow (maximum pressure) points, and slow down rotation ofrollers 16 on roller head 14 through known maximum flow (minimumpressure) points. This acceleration/deceleration profile can beadaptive; in other words, can vary depending upon cassette 18 and/or thesurgical parameters set by the user. For example, a set of pressure dataversus roller 16 position can be recorded by surgical console 112 usingsensor 126 and encoder 25 during initial priming or otherpre-operational tests of cassette 18. This data can be can be used toderive a pump speed profile required to achieve a desired pressure/flowprofile. The derived profile can be used to control the speed of pump 10during use. In addition, pressure data and position of roller 16 can becontinually monitored during use, and this data can be can be usedadaptively to vary the pump speed to achieve and maintain a desiredpressure/flow profile during surgery. Further, console 112 can beprogrammed with a variety of pressure/flow profiles previously generatedso as to optimize the pressure/flow profile for a particular cassettetype or surgical technique. The proper pressure/flow profile can bemanually selected by the user, or console 118 may automatically boot upsuch optimum pressure/flow profile by automatic identification of thecassette (e.g. barcode or RFID). All of these features can beimplemented on commercially available surgical equipment using softwarecommands well within a person skilled in the art.

Alternatively, sensor 126 may be used to predict minimum and maximumflow/pressure points based on the speed of motor shaft 12 so thatencoder 25 is not necessary.

As best seen in FIG. 4, which is plotting on the same scale as FIG. 3,optimization of the pressure/flow profile can result in greatlyattenuated peak to valley pressure variations, for example, on the orderof a 3 to 1 reduction.

This description is given for purposes of illustration and explanation.It will be apparent to those skilled in the relevant art thatmodifications may be made to the invention as herein described withoutdeparting from its scope or spirit. For example, the present inventionis also applicant to more conventional peristaltic pumps that stretch alength of tubing over the roller head.

1. A peristaltic pump, comprising: an adaptive variable speed control toaccelerate rotation of the pump through known minimum flow points, anddecelerate rotation of the pump through known maximum flow points. 2.The peristaltic pump of claim 1 wherein the acceleration anddeceleration of the peristaltic pump is based on a pump pulsationprofile, the pump pulsation profile being determined during initialpriming or other pre-operational test of the peristaltic pump.
 3. Theperistaltic pump of claim 1 wherein the acceleration and deceleration ofthe peristaltic pump is based on a pump pulsation profile, the pumppulsation profile being continually determined during operation of theperistaltic pump.
 4. The peristaltic pump of claim 1 wherein theacceleration and deceleration of the pump is based on a pump pulsationprofile, the pump pulsation profile being set by a user of theperistaltic pump.
 5. The peristaltic pump of claim 1 wherein theacceleration and deceleration of the peristaltic pump is based on a pumppulsation profile, the pump pulsation profile being determined byautomatic recognition of a cassette being used with the peristalticpump.
 6. A surgical console, comprising: a) a peristaltic pump, theperistaltic pump having a shaft and a roller head and a plurality ofroller mounted to the shaft; b) a position encoder associated with pumpfor establishing the location of the pump roller head and the pumprollers; c) a sensor for determining a pressure generated in anaspiration line by the peristaltic pump; and d) an adaptive variablespeed control, responsive to the position encoder and the pressuresensor to accelerate rotation of the pump rollers through known minimumflow/pressure points, and decelerate rotation of the pump rollersthrough known maximum flow/pressure points.
 7. The peristaltic pump ofclaim 6 wherein the acceleration and deceleration of the peristalticpump is based on a pump pulsation profile, the pump pulsation profilebeing determined during initial priming or other pre-operational test ofthe peristaltic pump.
 8. The peristaltic pump of claim 6 wherein theacceleration and deceleration of the peristaltic pump is based on a pumppulsation profile, the pump pulsation profile being continuallydetermined during operation of the peristaltic pump.
 9. The peristalticpump of claim 6 wherein the acceleration and deceleration of theperistaltic pump is based on a pump pulsation profile, the pumppulsation profile being set by a user of the peristaltic pump.
 10. Theperistaltic pump of claim 6 wherein the acceleration and deceleration ofthe peristaltic pump is based on a pump pulsation profile, the pumppulsation profile being determined by automatic recognition of acassette being used with the peristaltic pump.